ZW44 Tranny question

[mydementia]

Hey guys.  We're supposed to get 2-3 feet of snow with today's storm, so I took the day off and fired up the soldering iron.
Today's morning activity: the ZW44

I found the ZW44 vero layout on indyguitarist a while ago - looks like it's hosted here in Torchy's gallery now:
http://aronnelson.com/gallery/album28/ZAKK2?full=1

Subs:
1N4001 instead of the 1N4007
2N3904 instead of the MPSA14 (didn't know I'd need a darlington transistor)
20kB Pot for 20kW(B) -wasn't sure what a reverse-log-linear pot was???

The voltages on the op-amp are good and the tranny looks okay - but my output is VERY low.  I know petemoore had low output too (this thread: http://www.diystompboxes.com/smfforum/index.php?topic=34874.0) - did we make a bad tranny sub?  What about my diode sub?

I thought this simple circuit would be a slam-dunk...

Thanks for looking.
Mike

[Xavier]

I don't think the 2N3904 is a suitable sub for the MPSA14. I built mine following the same schematic and layout with the right MPSA14 and I have plenty of output.

The 2N3904 is not a darlington, let alone being a high gain transistor neither. This is my guess....

[jrc4558]

Without having looked at the schem - I think transistor has nothing to do with it if its an input buffer. Input buffer is a unity gain module and will not affect the output volume.

[Joep]

The input transistor is a configured as an input buffer with unity gain as said in the previous post. But because of the (ultra) high Hfe of the darlington, the input impedance is higher as a "normal" input buffer with 2N3904 or alikes. This will effect tone! (unless you use active pickup system) Cable capacitance will be of less influence resulting in a clearer (more highs) tone. The MPSA14 in this way is important in the sound of the ZW-44. But other types will work.

Did you check the 2N3904 bias? The relative high bias resistors (2M2 and 1M) might not work properly with the 2N3904 which results in a not proper biased 2N3904.

Joep

[jimbob]

IS there anyting special about this zw44 or is it just another run of the mill distortion pedal?

[$uperpuma]

nothing super special... but it does have a nice sound... gringo did a nice, small layout for it... I like the ease of pinch harmonics with it... oh.. and as stated above, you'll need a darlington device for that tranny... a single trans won't get it, as designed. the diode change shouldn't make a drastic change.

[mydementia]

Thanks guys - I'll get the right tranny next time I can go somewhere (this storm turned into a blizzard )
Mike

[R.G.]

2N3904 instead of the MPSA14 (didn't know I'd need a darlington transistor)

The suspicion is correct - the 2N3904 is not a darlington, and may not provide good enough function.

But two of them might. Hook up two 2N3904s in a discrete darlington. Hook both collectors together, hook one emitter to the base of the other. The collectors are the collector of the new darlington, the free base is the base, and the free emitter is the emitter. It's not perfect, but it may work until you can get an integrted darlington.

[MikeH]

This was one of my first builds, and I was having trouble finding an MPSA14.  Someone emailed me this list of suitable alternatives:

MPSA13
2N5305
BC517
BC617
MPSA12
ECG46
ECG172A
2SC982
2SC1472K 
2N5525
2N5306

[Somicide]

IIRC, the ZW44 is a "modded" version of the BOSS SD-1 he used to use.  Could be wrong, but I swear I read that somewhere.

[Joep]

it is!

[Somicide]

thought so; that was his primary lead boost, no?  I'm not the biggest fan of ZW, though he is awesome ("In this River," or whatever is called, was a great tribute to Dime.)

[JHS]

I used a National LM353N w JFET-input, (input impedance set to 220k) and dropped the inputbuffer, works great and sounds good.
The lower input impedance add some slight compression like the buffer. A common IC-buffer w TL 071C is a good subs too and generate lower hiss compared to a MPSA18 buffer.

JHS

[mydementia]

SUCCESS
I got an NTE46 from my local surplus store - plugged it in - and still had very low output...
Got out the DMM and started probing the strips to find where the signal was getting sucked to ground - found it.  Once I got the tranny oriented properly (yep, one rookie mistake right after another on this build!!) I was rocking. 

My build of the ZW44 is a VERY nice overdrive - a lot of compression at full gain and treb - likely where I'll use this most.  I haven't tried this in front of an already distorted signal...but I'm guessing it's going to be sweet. 

MartyMart - you've built pretty much EVERY other noise box out there - I recommend this one!!
Mike

[rama claproth]

If you have an SD1 boss pedal, you can convert it into MXR ZW44 specs!

1. Remove one leg of the resistor 33K (R5) that goes with 4K7 (R6) and connect to the diode's leg (D1) that goes to pin 7 at the opamp chip. Remove yellow wire # 4 at the PCB and also remove red wire # 2. Connect yellow wire at # 2, # 4 stays EMPTY. Connect red wire to where the 33K resistor's leg USED to stay that connects with the resistor 4K7 at R6, now this automatically goes to the opamp at pin 6.

2. Replace C4 with a 0.047uF capacitor.

3. Replace C5 with a 0.047uF capacitor.

4. Replace R3 with a 22K resistor.

5. Replace C7 with a 3.3uF capacitor.

6. Remove Q6, R15, R16, R17, and C10. These NO NEED jumpers. The white wire # 12 at the PCB must be removed and has to be connected into the hole where the base pin of Q6 used to stay.

7. Remove brown wire # 1 at the PCB and connect into ground.

8. Change Q5 with MPSA14 transistor. This is OPTIONAL.

DONE!